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Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems.

Gao T, Shen Y, Jia Z, Qiu G, Liu F, Zhang Y, Feng X, Cai C - Geochem. Trans. (2015)

Bottom Line: The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite.The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days.The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan, 430070 People's Republic of China.

ABSTRACT

Background: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.

Results: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn(2+) and K(+) ions, a significant decrease in Fe(2+) concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe(2+) exhibited much higher catalytic activity than Mn(2+) during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn(2+) were compared to estimate the redox rates of birnessite and Fe(2+) under different conditions.

Conclusions: Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe(2+) concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe(2+) to ferric oxides. Graphical abstract:Lepidocrocite and goethite were formed during the interaction of ferrous ion and birnessite at pH 4-7. Redox rate was controlled by the adsorption of Fe2+ on the surface of birnessite. The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

No MeSH data available.


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XRD patterns of solid products of 10 mMFe2(SO4)3 (a),Fe2(SO4)3(10 mM)/MnSO4 (10 mM) (b), andFe2(SO4)3(10 mM)/FeSO4 (10 mM) (c) aqueous solutionsin nitrogen atmosphere with pH 5.5 at different times
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Fig6: XRD patterns of solid products of 10 mMFe2(SO4)3 (a),Fe2(SO4)3(10 mM)/MnSO4 (10 mM) (b), andFe2(SO4)3(10 mM)/FeSO4 (10 mM) (c) aqueous solutionsin nitrogen atmosphere with pH 5.5 at different times

Mentions: Figure 6 shows the XRD patterns of solidproducts of Fe2(SO4)3(10 mmol L−1),Fe2(SO4)3(10 mmol L−1)/MnSO4(10 mmol L−1), andFe2(SO4)3(10 mmol L−1)/FeSO4(10 mmol L−1) aqueous solutions in nitrogen atmosphere with pH 5.5 atdifferent times. As forFe2(SO4)3 aqueous solution,amorphous ferric (hydr)oxide was formed at pH 5.5, and its crystallinity did not obviously increaseafter 25 days. The addition of Mn2+ facilitated the formation of amixture of lepidocrocite and goethite, and the latter was major product after 25 days(Fig. 6b). The presence of Fe2+significantly accelerated the formation of lepidocrocite and goethite, which were observed after1 days (Fig. 6c). Lepidocrocite was the major product in theinitial stage, and would slowly transform into goethite, which was indicated by the relative changein the intensity of XRD peaks. These results exhibited that Fe2+ hadhigher catalytic activity than Mn2+ for the formation of crystallineferric oxides, and further suggested that not all transition metal ions inhibited the formation ofgoethite from lepidocrocite, which was likely due to the particular affinity and constant pH duringthis reaction process [2, 31, 38].Fig. 6


Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems.

Gao T, Shen Y, Jia Z, Qiu G, Liu F, Zhang Y, Feng X, Cai C - Geochem. Trans. (2015)

XRD patterns of solid products of 10 mMFe2(SO4)3 (a),Fe2(SO4)3(10 mM)/MnSO4 (10 mM) (b), andFe2(SO4)3(10 mM)/FeSO4 (10 mM) (c) aqueous solutionsin nitrogen atmosphere with pH 5.5 at different times
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC4585411&req=5

Fig6: XRD patterns of solid products of 10 mMFe2(SO4)3 (a),Fe2(SO4)3(10 mM)/MnSO4 (10 mM) (b), andFe2(SO4)3(10 mM)/FeSO4 (10 mM) (c) aqueous solutionsin nitrogen atmosphere with pH 5.5 at different times
Mentions: Figure 6 shows the XRD patterns of solidproducts of Fe2(SO4)3(10 mmol L−1),Fe2(SO4)3(10 mmol L−1)/MnSO4(10 mmol L−1), andFe2(SO4)3(10 mmol L−1)/FeSO4(10 mmol L−1) aqueous solutions in nitrogen atmosphere with pH 5.5 atdifferent times. As forFe2(SO4)3 aqueous solution,amorphous ferric (hydr)oxide was formed at pH 5.5, and its crystallinity did not obviously increaseafter 25 days. The addition of Mn2+ facilitated the formation of amixture of lepidocrocite and goethite, and the latter was major product after 25 days(Fig. 6b). The presence of Fe2+significantly accelerated the formation of lepidocrocite and goethite, which were observed after1 days (Fig. 6c). Lepidocrocite was the major product in theinitial stage, and would slowly transform into goethite, which was indicated by the relative changein the intensity of XRD peaks. These results exhibited that Fe2+ hadhigher catalytic activity than Mn2+ for the formation of crystallineferric oxides, and further suggested that not all transition metal ions inhibited the formation ofgoethite from lepidocrocite, which was likely due to the particular affinity and constant pH duringthis reaction process [2, 31, 38].Fig. 6

Bottom Line: The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite.The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days.The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan, 430070 People's Republic of China.

ABSTRACT

Background: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.

Results: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn(2+) and K(+) ions, a significant decrease in Fe(2+) concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe(2+) exhibited much higher catalytic activity than Mn(2+) during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn(2+) were compared to estimate the redox rates of birnessite and Fe(2+) under different conditions.

Conclusions: Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe(2+) concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe(2+) to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe(2+) to ferric oxides. Graphical abstract:Lepidocrocite and goethite were formed during the interaction of ferrous ion and birnessite at pH 4-7. Redox rate was controlled by the adsorption of Fe2+ on the surface of birnessite. The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite.

No MeSH data available.


Related in: MedlinePlus